Agriculturalists have to work with all types of plant growth media such as sand, natural earth, horticultural soils, and various soil-mimicking, soil-less plant culture substrates; however, the bane of essentially all agriculturalists is water repellent soil. Water repellent soil retards water infiltration into the soil matrix and often renders entire areas of the upper layers of the soil substrate essentially impervious to water penetration. Under rainfall or irrigation conditions, dire environmental consequences can result from the water repellency of the topsoil, such as surface runoff of water and aqueous compositions containing pesticides, this term inclusive of fertilizers, into pristine areas and/or potable reservoirs. Furthermore, and less obvious, are the serious consequences that result from aqueous pesticide flow through “fingers” that usually attend water repellent soil which can provide rapid transport of pesticide compositions to the local ground water table and thus increase the risk of ground water contamination.
Water repellency of a soil is not only a function of the initial water content of the soil, but is also a function of soil particle size (sands are more prone to water repellency than clays), as well as, type of organic matter incorporated in it. This organic matter induces water repellency in the soils in many ways, such as by providing hydrophobic organic substances leached from the plant litter; organic substances that have been irreversibly dried; and microbial by-products.
Before water will evenly infiltrate into or percolate through a soil matrix, there must be a continuous film of water on the soil particles. In other words, the soil must first be wetted before water will flow. In addition, getting the soil evenly wetted is of paramount importance to the healthy growth of plants or seeds which are to be grown in the soil. Thus, agriculturalists will often apply various wetting agent surfactant compositions directly to the soil or admix same with aqueous pesticide formulations to reduce the surface tension of the composition before applying the pesticide to the plant growth media as taught, for example, in U.S. Pat. No. 2,867,944; U.S. Pat. No. 5,595,957; U.S. Pat. No. 5,385,750; WO 96/34078; and WO 98/39273.
“Although an increasing number of researchers are aware of the occurrence and consequences of water repellency in a wide range of soils, it is still a neglected field in soil science.” (Dekker et al., International Turfgrass Society Research Journal, Volume 9, 2001, pages 498-505)
It has been recognized for years that in water repellent soil significant spatial variability can occur both in soil water content and degree of water repellency. Agriculturalists have attacked the soil water repellency problem through the use of wetting agent surfactant compositions. The degree of efficacy among chemistries and formulations have varied significantly. Often, the amount of surfactant required to ameliorate water repellency and/or to enhance infiltration, either perform variably or in an attempt to improve performance, higher rates of wetting agents are applied, such elevated rates often becoming injurious to plants.
Thus, there is a continuing search for wetting agent compositions with increased wetting rate that are able to quickly penetrate and infiltrate the water repellent soil. The use of wetting agent compositions with increased wetting rates, in turn, will result in a more effective wetting of the root zone during rain events and/or irrigation applications, thereby, inducing better plant growth and decreased run-off.